Efficient and regulated nucleocytoplasmic trafficking of macromolecules to the correct subcellular compartment is critical for proper functions of the eukaryotic cell. The majority of the macromolecular traffic across the nuclear pores is mediated by the Karyopherin-β (or Kap) family of nuclear transport receptors. Work over more than two decades has shed considerable light on how the different Kap family members bring their respective cargoes into the nucleus or the cytoplasm in efficient and highly regulated manners. In this Review, we overview the main features and established functions of Kap family members, describe how Kaps recognize their cargoes and discuss the different ways in which these Kap–cargo interactions can be regulated, highlighting new findings and open questions. We also describe current knowledge of the import and export of the components of three large gene expression machines — the core replisome, RNA polymerase II and the ribosome — pointing out the questions that persist about how such large macromolecular complexes are trafficked to serve their function in a designated subcellular location.

将大分子有效且受监管的核质运输到正确的亚细胞区室对于真核细胞的正常功能至关重要。大多数穿过核孔的大分子运输是由核转运受体 Karyopherin-β（或 Kap）家族介导的。二十多年来的工作已经阐明了不同的 Kap 家族成员如何以高效和高度监管的方式将各自的货物带入细胞核或细胞质。在这篇综述中，我们概述了 Kap 家族成员的主要特征和既定功能，描述了 Kaps 如何识别他们的货物，并讨论了这些 Kap-货物相互作用可以被监管的不同方式，突出了新发现和悬而未决的问题。